A10. The Quads – Polar Caps (North & South)
Shared polar themes (both caps)
Layered climate archives. Millennia-to-Myr layering encodes obliquity-driven climate cycles; SHARAD/MARSIS radar stratigraphy shows largely water-ice stacks with dust bands.
Seasonal caps. Each winter, a seasonal CO₂ cap (~1 m scale) condenses and sublimes in spring; its mass exchange drives ~25–30% swings in global surface pressure and produces striking defrost patterns.
Winds & troughs. Katabatic winds, twisted by Coriolis, are implicated in the formation of spiral troughs and the maintenance of cap asymmetries.
Dunes & dust. Circumpolar ergs (notably Olympia Undae in the north) testify to sustained aeolian transport; dust mantles and polar hoods strongly control insolation at the ground.
⚫ North Polar (N) — Planum Boreum & surroundings
Profile. A circular polar plateau (Planum Boreum) ~1,000–1,200 km across, underlain by north polar layered deposits (NPLD) of water ice and dust. The cap is incised by spiral troughs and the canyon Chasma Boreale, and it is partly encircled by the vast dune sea Olympia Undae. The plateau sits within the northern lowlands (Vastitas Borealis).
Relief & elevation (context). The surrounding northern lowlands lie near ~−5 km (areoid). The polar plateau rises a few km above those plains; typical cap-surface elevations are ~−3 to −2 km. Local relief of trough walls/cliffs commonly reaches hundreds of meters to ~2 km in Chasma Boreale.
Stratigraphy & composition.The NPLD are ~2 km thick in places and are overwhelmingly water ice with only minor dust (≲ a few percent), stacked as thousands of thin layers that archive climate cycles. A thin seasonal CO₂ frost veneer (order ~1 m at high latitudes) forms each winter and sublimates in spring.
Landforms. Spiral troughs (katabatic-wind–shaped; Coriolis-twisted) and the ~500 km-long, ~2 km-deep Chasma Boreale nearly bisect the cap. Dune seas (notably Olympia Undae, ~470,000 km²) ring parts of the plateau.
Surface texture. Bright, smooth ice interleaved with dark, dusty trough walls; steep scarps exposing layered strata; ergs of dark basaltic sand (megaripples, barchans) along the cap margin.
Atmosphere, light & “weather”. Polar hood: seasonal water-ice cloud deck forms and dissipates around cap edges; spring defrosting drives strong thermal contrasts and dust lifting. During dusty periods, direct sunlight drops and blue-tinged scattering near the Sun becomes pronounced at low solar elevations.
Numbers at a glance. NPLD thickness to ~2 km; residual summer cap ~1,000 km in diameter. Olympia Undae ≈ 470,000 km²; Chasma Boreale ~500 km × 2 km deep. Total north polar water-ice volume estimated at ~1.2–1.7 million km³.
⚫ South Polar (-S) — Planum Australe & surroundings
Profile. The Planum Australe plateau hosts thick south polar layered deposits (SPLD) with a distinctive permanent CO₂ veneer (the Residual South Polar Cap, RSPC) overlying water ice. The region is dissected by large canyons (Chasma Australe; Promethei; Ultimum) and flanked by circumpolar dune fields on the surrounding highlands. Wikipediamarsed.asu.edu
Relief & elevation (context). The south polar dome is ~3 km above adjacent terrain and is offset from the geographic pole by a few hundred km; the plateau itself stands several km above the areoid on the southern highlands. Basin–rim contrasts yield dramatic slopes and scarps.
Stratigraphy & composition. SPLD thickness reaches ~3–3.5 km; the RSPC is a thin (≈ 8–10 m) CO₂ ice layer draped atop water-ice deposits. Radar has revealed massive, buried CO₂ ice bodies within the south cap (kilometer-scale sequences) in addition to the dominant water ice.
Landforms. Chasma Australe (order ~500 km long) and companion canyons incise the SPLD; spiral troughs are present as in the north. The periphery hosts extensive dune belts (less continuous than Olympia Undae), and some crater basins (e.g., McMurdo) display complex intracap stratigraphy. “Cryptic terrain” often emerges during spring defrost.
Surface texture. Bright layered ice, steep scarp exposures, dark dust-lag patches and seasonal slab-ice patterns; surrounding highlands exhibit yardangs and dune fields aligned with katabatic-wind corridors.
Atmosphere, light & “weather.” Seasonal CO₂ snowfall/frost expands equatorward to ~60°S at winter peak; spring sublimation triggers jet-like “spider” activity through translucent slab ice, entraining dark sand. Polar hoods and dust hazes modulate lighting from crisp, high-contrast scenes to sepia, diffuse illumination.
Numbers at a glance. SPLD thickness ~3–3.5 km; RSPC ~8–10 m CO₂; south polar ice + layered deposits volume ~1.6 million km³ (water ice). Major canyons ~500 km long; dome apex offset ~150–250 km from the pole.